Electrochemical Studies Of Vanadium Oxides For Use In Lithium Batteries

Vanadium oxides of varying stoichiometries have been studied for their potential use in rechargeable solid state lithium batteries. Deposits of hydrated diammonium hexavanadates have been prepared electrochemically on various conducting anode substrates. Coherent electrodeposits of highly oriented, crystalline M{dollar}\sb4{dollar}V{dollar}\sb6{dollar}O{dollar}\sb{lcub}16+\delta{rcub}{dollar}, where M = NH{dollar}\sb4{dollar}, K, Rb and Cs and 0.00 {dollar}\u3c\delta\u3c{dollar} 0.10, have also been made for the first time electrochemically on various conducting cathode substrates. Also, mixed crystalline phases of formula M{dollar}\sb{lcub}4-X{rcub}{dollar}N{dollar}\sb{lcub}X{rcub}{dollar}V{dollar}\sb6{dollar}O{dollar}\sb{lcub}16+\delta{rcub}{dollar}, where M, N = NH{dollar}\sb4{dollar}, K, Rb and Cs, M {dollar}\not={dollar} N and 0.00 {dollar}\u3c\delta\u3c{dollar} 0.13, have been made. The mechanism of formation of a deposit at the anode involves formation of a hydrated V{dollar}\sb2{dollar}O{dollar}\sb5{dollar} sol in a pH gradient at the anode, and subsequent electrophoretic deposition of the sol as an oriented crystalline deposit. The sol spreads to the cathode by convection, migration and diffusion, where the particles adhere with evidence of nucleation and growth on the cathode. These electrodeposits have been studied using both electrochemical and non-electrochemical techniques to determine their structure, stoichiometry and use as reversible insertion electrodes.;The deposits containing NH{dollar}\sb4\sp+{dollar} can be decomposed to crystalline V{dollar}\sb2{dollar}O{dollar}\sb5{dollar} by heating in air, or to non-stoichiometric V{dollar}\sb6{dollar}O{dollar}\sb{lcub}13{rcub}{dollar} by heating in argon or in vacuum at 300{dollar}\sp\circ{dollar}C for several hours, with retention of their orientation on the substrate. The first step of the thermal decomposition involves loss of 2NH{dollar}\sb3{dollar} + H{dollar}\sb2{dollar}O. In the second step, on heating in air, recrystallization and oxidation of V(IV) to V(V) is observed with the addition of 1/2 O to form V{dollar}\sb2{dollar}O{dollar}\sb5{dollar}. This oxidation is not seen on heating under reduced O{dollar}\sb2{dollar} partial pressure and reduction continues until V{dollar}\sb6{dollar}O{dollar}\sb{lcub}13+\delta{rcub}{dollar} is formed, where {dollar}\delta{dollar} is a function of how much residual O{dollar}\sb2{dollar} is left exposed to the deposit. Lithium could be reversibly inserted into and removed from the V{dollar}\sb2{dollar}O{dollar}\sb5{dollar} form of the deposit up to a mole ratio Li/V{dollar}\sb2{dollar}O{dollar}\sb5{dollar} = 1.2. For non-stoichiometric V{dollar}\sb6{dollar}O{dollar}\sb{lcub}13{rcub}{dollar} the ratio of Li/V{dollar}\sb6{dollar}O{dollar}\sb{lcub}13{rcub}{dollar} = 4.4. However, electrodes that were not decomposed inserted only a small amount of lithium, {dollar}\u3c{dollar}1% of total V.;Single-cell batteries consisting of a Li anode, a polymer electrolyte such as MEEP, PEO or tetraglyme (supported in Celgard) and a vanadium pentoxide cathode have been studied. The batteries show favorable cycle lifetimes and high cathode capacity